JP2010267638A - Method for coating protective film and method for laser processing of wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for coating a protective film capable of uniformly coating a wafer with a protective film.
A method of coating a protective film for coating a processed surface of a wafer with a protective film made of a water-soluble resin, the holding table having a holding surface for holding a wafer, wherein the non-processed surface side of the wafer is the holding surface. A wafer holding step for holding the wafer in opposition to the wafer, and a hydrophilicity imparting step for generating ozone by irradiating the processed surface of the wafer with ultraviolet rays and generating active oxygen to impart hydrophilicity to the processed surface; And a protective film coating step of coating the protective film by applying a water-soluble resin to the processed surface to which hydrophilicity has been imparted.
[Selection] Figure 7

Description

  The present invention relates to a protective film coating method for coating a water-soluble resin protective film on the surface of a wafer such as a semiconductor wafer or an optical device wafer.

  A wafer such as a silicon wafer or a sapphire wafer formed on the surface by dividing a plurality of devices such as IC, LSI, LED, etc. by dividing lines is divided into individual devices by a processing apparatus, and the divided devices are mobile phones, Widely used in various electronic devices such as personal computers.

  A dicing method using a cutting device called a dicer is widely used for dividing the wafer. In the dicing method, a wafer is cut by cutting a wafer into a wafer while rotating a cutting blade having a thickness of about 30 μm by solidifying abrasive grains such as diamond with a metal or a resin at a high speed of about 30000 rpm. Divide into

  On the other hand, in recent years, a laser processing groove is formed by irradiating a wafer with a pulsed laser beam having a wavelength that absorbs the wafer, and the wafer is cut along the laser processing groove by a breaking device. A method of dividing into devices has been proposed (see, for example, Japanese Patent Laid-Open No. 10-305420).

  The formation of the laser processing groove by the laser processing apparatus can increase the processing speed as compared with the dicing method using the dicer, and relatively easily processes even a wafer made of a material having high hardness such as sapphire or SiC. be able to. In addition, since the processing groove can be made to have a narrow width of, for example, 10 μm or less, the amount of devices taken per wafer can be increased as compared with the case of processing by the dicing method.

  However, when the wafer is irradiated with a pulse laser beam, debris is generated due to concentration of thermal energy in the region irradiated with the pulse laser beam. When this debris adheres to the device surface, there arises a problem that the quality of the device is lowered.

  Therefore, for example, in JP 2007-201178 A, a water-soluble resin such as PVA (polyvinyl alcohol) or PEG (polyethylene glycol) is applied to the processed surface of the wafer in order to solve such problems caused by debris. There has been proposed a laser processing apparatus in which a protective film is coated and a wafer is irradiated with a pulse laser beam through the protective film.

JP-A-10-305420 JP 2007-2011178 A

  However, there is a problem that it is difficult to uniformly cover the entire processed surface of the wafer because the processed surface of the wafer includes a hydrophilic region having a hydrophilic property and a hydrophobic region having a hydrophobic property. is there.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a method of coating a protective film that can uniformly coat the processed surface of the wafer.

  According to the present invention, there is provided a protective film coating method for coating a processed surface of a wafer with a protective film made of a water-soluble resin, the holding table having a holding surface for holding a wafer, and holding the non-processed surface side of the wafer A wafer holding step for holding the wafer facing the surface, and a hydrophilicity imparting step for imparting hydrophilicity to the processed surface by generating ozone by irradiating the processed surface of the wafer with ultraviolet rays to generate ozone. And a protective film coating step of coating the protective film by applying a water-soluble resin to the processed surface imparted with hydrophilicity.

  Preferably, in the protective film coating step, the water-soluble resin is dropped onto the central region of the processed surface of the wafer while rotating the holding table.

  According to the present invention, since the entire processed surface of the wafer is processed to be hydrophilic before coating the protective film, the protective film can be uniformly coated.

It is a flowchart which shows each step of embodiment of this invention. It is an external appearance perspective view of a laser processing apparatus. It is a perspective view which shows the wafer supported by the annular frame via the dicing tape. It is a block diagram of a laser beam irradiation unit. It is a partially broken perspective view of a protective film coating apparatus. It is a longitudinal cross-sectional view of the protective film coating apparatus in a state where the spinner table is raised and the wafer is held on the spinner table. It is a longitudinal cross-sectional view of the protective film coating apparatus in a state where the spinner table is lowered and the wafer is irradiated with ultraviolet rays. It is a longitudinal cross-sectional view of the protective film coating | coated apparatus of the state which apply | coats water-soluble resin to the wafer surface. It is an expanded sectional view of a wafer with which a protective film was covered. It is explanatory drawing which shows a laser processing step. It is a longitudinal cross-sectional view of the protective film coating apparatus which shows the washing | cleaning step (protective film removal step). It is an expanded sectional view of a wafer in the state where a protective film was removed by a washing step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, a protective film coating method and a laser processing method according to an embodiment of the present invention will be schematically described with reference to a flowchart of FIG.

  In the protective film coating method of the present invention, first, in step S10, the non-processed surface side of the wafer is held by a holding table having a rotation axis passing through the center of the holding surface and orthogonal to the holding surface holding the wafer. Next, in step S11, the processed surface of the wafer is irradiated with ultraviolet rays to generate ozone and generate active oxygen to impart hydrophilicity to the entire processed surface.

  After imparting hydrophilicity to the processed surface of the wafer in this way, a water-soluble resin is applied to the processed surface of the wafer to which hydrophilicity has been imparted in step S12 to cover the protective film. After the processing surface of the wafer is coated with a protective film, a laser processing groove is formed by irradiating the processing surface of the wafer with a pulsed laser beam in step S13.

  This laser beam for processing is a pulse laser beam having absorptivity with respect to the wafer. For example, a pulse laser beam having a wavelength of 355 nm, which is the third harmonic of a YAG laser, is used.

  After forming the laser processing groove on the wafer, the wafer is divided into individual devices by cleaving the wafer along the laser processing groove with a braking device. Thereafter, in step S14, cleaning water is sprayed onto the wafer surface to remove the protective film.

  Hereinafter, a protective film coating apparatus suitable for carrying out the protective film coating method of the present invention will be described in detail. FIG. 2 shows an appearance of a laser processing apparatus 2 that includes a protective film coating apparatus and can divide the wafer into individual chips (devices) by laser processing.

  On the front side of the laser processing apparatus 2, operation means 4 is provided for an operator to input instructions to the apparatus such as processing conditions. In the upper part of the apparatus, there is provided a display means 6 such as a CRT for displaying a guidance screen for an operator and an image taken by an imaging means described later.

  As shown in FIG. 3, on the surface of the semiconductor wafer W to be processed, the first street S1 and the second street S2 are formed orthogonally, and the first street S1 and the second street S2 are formed. A number of devices D are formed in a region partitioned by.

  The wafer W is attached to a dicing tape T that is an adhesive tape, and the outer peripheral edge of the dicing tape T is attached to an annular frame F. As a result, the wafer W is supported by the annular frame F via the dicing tape T, and a plurality of wafers (for example, 25 sheets) are accommodated in the wafer cassette 8 shown in FIG. The wafer cassette 8 is placed on a cassette elevator 9 that can move up and down.

  Behind the wafer cassette 8, loading / unloading means 10 is provided for unloading the wafer W before laser processing from the wafer cassette 8 and loading the processed wafer into the wafer cassette 8.

  Between the wafer cassette 8 and the loading / unloading means 10, a temporary placement area 12, which is an area on which a wafer to be loaded / unloaded is temporarily placed, is provided. A wafer W is fixed in the temporary placement area 12. Positioning means 14 for positioning to the position of is arranged.

  Reference numeral 30 denotes a protective film coating apparatus. The protective film coating apparatus 30 also serves as a cleaning apparatus for cleaning the processed wafer. In the vicinity of the temporary placement region 12, a transport unit 16 having a turning arm that sucks and transports the frame F integrated with the wafer W is disposed.

  The wafer W carried out to the temporary placement area 12 is adsorbed by the transport means 16 and transported to the protective film coating apparatus 30. In the protective film coating apparatus 30, the protective film is coated on the processed surface of the wafer W as will be described in detail later.

  Adjacent to the protective film coating apparatus 30 is provided an ultraviolet irradiation device 35 that irradiates the wafer surface with ultraviolet rays before forming a protective film on the wafer surface. The ultraviolet irradiation device 35 is supported by an arm 39 and is movable between the retracted position shown in FIG. 2 around the base end portion of the arm 39 and the ultraviolet irradiation position overlapping the upper surface of the protective film coating device 30. It is.

  The wafer W whose processing surface is coated with a protective film is attracted by the conveying means 16 and conveyed onto the chuck table 18 and is sucked by the chuck table 18, and the frame F is fixed by a plurality of fixing means (clamps) 19. As a result, the chuck table 18 is held.

  The chuck table 18 is configured to be rotatable and reciprocally movable in the X-axis direction. Above the movement path of the chuck table 18 in the X-axis direction, an alignment unit 20 that detects a street of the wafer W to be laser processed. Is arranged.

  The alignment unit 20 includes an imaging unit 22 that images the surface of the wafer W, and can detect a street to be laser processed by image processing such as pattern matching based on an image acquired by imaging. The image acquired by the imaging unit 22 is displayed on the display unit 6.

  A laser beam irradiation unit 24 that irradiates the wafer W held on the chuck table 18 with a laser beam is disposed on the left side of the alignment means 20. The laser beam irradiation unit 24 is movable in the Y axis direction.

  The casing 26 of the laser beam irradiation unit 24 accommodates laser beam oscillation means and the like which will be described in detail later, and a condenser (a light collector for condensing the laser beam on the wafer to be processed) at the tip of the casing 26. A laser head) 28 is attached.

  As shown in the block diagram of FIG. 4, a laser beam oscillating means 34 and a laser beam modulating means 36 are disposed in the casing 26 of the laser beam irradiation unit 24.

  As the laser beam oscillation means 34, a YAG laser oscillator or a YVO4 laser oscillator can be used. The laser beam modulating unit 36 includes a repetition frequency setting unit 38, a laser beam pulse width setting unit 40, and a laser beam wavelength setting unit 42.

  The repetition frequency setting means 38, the laser beam pulse width setting means 40, and the laser beam wavelength setting means 42 constituting the laser beam modulation means 36 are of known forms, and detailed description thereof is omitted in this specification.

  The wafer W that has been subjected to laser processing by the laser beam irradiation unit 24 is held by the conveying means 32 that can move in the Y-axis direction after the chuck table 18 is moved in the X-axis direction, and is also covered with a protective film. It is conveyed to the device 30. The protective film coating apparatus 30 cleans the wafer by rotating the wafer W at a low speed (for example, 300 rpm) while spraying water from the cleaning nozzle.

  After cleaning, the wafer W is dried at a high speed (for example, 2000 rpm) by blowing air from the air nozzle to dry the wafer W, and then the wafer W is adsorbed by the conveying means 16 and returned to the temporary storage area 12, and then the loading / unloading means 10, the wafer W is returned to the original storage location of the wafer cassette 8.

  Next, a protective film coating apparatus 30 suitable for carrying out the protective film coating method of the present invention will be described with reference to FIGS. First, referring to FIG. 5, a partially broken perspective view of the protective film coating apparatus 30 is shown.

  The protective film coating apparatus 30 includes a spinner table mechanism 44 and a cleaning water receiving mechanism 46 that surrounds the spinner table mechanism 44. The spinner table mechanism 44 includes a spinner table (holding table) 48, an electric motor 50 that rotationally drives the spinner table 48, and a support mechanism 52 that supports the electric motor 50 so as to be movable in the vertical direction.

  The spinner table 48 includes a suction chuck (holding surface) 48a formed of a porous material, and the suction chuck 48a communicates with suction means (not shown). Accordingly, the spinner table 48 holds the wafer on the suction chuck 48a by placing the wafer on the suction chuck 48a and applying a negative pressure by suction means (not shown).

  The spinner table 48 is provided with a pair of pendulum type clamps 49. When the spinner table 48 is rotated, the clamp 49 swings by centrifugal force to clamp the annular frame F shown in FIG.

  The spinner table 48 is connected to the output shaft 50 a of the electric motor 50. The support mechanism 52 includes a plurality of (three in the present embodiment) support legs 54 and a plurality of (three in the present embodiment) air cylinders 56 respectively connected to the support legs 54 and attached to the electric motor 50. It consists of.

  The support mechanism 52 configured in this manner operates the air cylinder 56 to move the electric motor 50 and the spinner table 48 at the wafer loading / unloading position, which is the ascending position shown in FIG. 6, and the machining position shown in FIG. It can be positioned at a certain work position.

  The cleaning water receiving mechanism 46 is attached to the cleaning water receiving container 58, three support legs 60 (only two are shown in FIG. 4) that support the cleaning water receiving container 58, and the output shaft 50 a of the electric motor 50. Cover member 62.

  As shown in FIGS. 6 and 7, the cleaning water receiving container 58 includes a cylindrical outer wall 58a, a bottom wall 58b, and an inner wall 58c. A hole 51 into which the output shaft 50a of the electric motor 50 is inserted is provided at the center of the bottom wall 58b, and the inner wall 58c is formed so as to protrude upward from the periphery of the hole 51.

  Further, as shown in FIG. 5, a waste liquid port 59 is provided in the bottom wall 58 b, and a drain hose 64 is connected to the waste liquid port 59. The cover member 62 is formed in a disc shape, and includes a cover portion 62a that protrudes downward from the outer periphery thereof.

  When the electric motor 50 and the spinner table 48 are positioned at the work position shown in FIGS. 7 and 8, the cover member 62 configured in this way is located outside the inner wall 58 c that constitutes the cleaning water receiving container 58. It is positioned so as to polymerize with a gap.

  The protective film coating apparatus 30 includes an application unit 66 that applies a water-soluble resin to the unprocessed wafer W held by the spinner table 48. The application unit 66 includes a water-soluble resin supply nozzle 68 that supplies a water-soluble resin toward the processed surface of the wafer before processing held by the spinner table 48, and a substantially L-shaped arm that supports the water-soluble resin supply nozzle 68. 70 and an electric motor 72 capable of normal / reverse rotation that swings the water-soluble resin supply nozzle 68 supported by the arm 70. The water-soluble resin supply nozzle 68 is connected to a water-soluble resin supply source (not shown) via the arm 70.

  The protective film coating apparatus 30 also serves as a cleaning apparatus for cleaning the wafer after laser processing. Therefore, the protective film coating apparatus 30 includes cleaning water supply means 74 and air supply means 76 for cleaning the processed wafer held on the spinner table 48.

  The cleaning water supply means 74 includes a cleaning water nozzle 78 that ejects cleaning water toward the processed wafer held by the spinner table 48, an arm 80 that supports the cleaning water nozzle 78, and a cleaning that is supported by the arm 80. The electric motor 82 is configured to be able to rotate normally and reversely so as to swing the water nozzle 78. The cleaning water jet nozzle 78 is connected to a cleaning water supply source (not shown) via the arm 80.

  The air supply means 76 includes an air nozzle 84 that blows air toward the cleaned wafer held by the spinner table 48, an arm 86 that supports the air nozzle 84, and a positive that swings the air nozzle 84 that is supported by the arm 86. An electric motor (not shown) capable of rotating and reversing is provided. The air nozzle 84 is connected to an air supply source (not shown) via an arm 86.

  As shown in FIG. 5, an ultraviolet irradiation device 35 is rotatably provided above the protective film coating device 30. As shown in FIG. 7, the ultraviolet irradiation device 35 has a plurality of ultraviolet lamps 37.

  Next, the operation of the protective film coating apparatus 30 and the ultraviolet irradiation apparatus 35 configured as described above will be described. The wafer before processing is transported to the spinner table 48 of the protective film coating apparatus 30 by the turning motion of the wafer transport means 16, and is sucked and held by the suction chuck 48a as shown in FIG.

  At this time, the water-soluble resin supply nozzle 68, the washing water nozzle 78, and the air nozzle 84 are positioned at a standby position separated from above the spinner table 48, as shown in FIGS.

  When the wafer W is sucked and held by the spinner table 48, the ultraviolet irradiation device 35 is rotated and the ultraviolet irradiation device 35 is positioned so as to cover the protective film coating device 30 as shown in FIG. Then, the ultraviolet lamp 37 is turned on to irradiate the surface (processed surface) of the wafer W with ultraviolet rays to generate ozone and generate active oxygen to impart hydrophilicity to the processed surface of the wafer W.

  After imparting hydrophilicity to the processed surface of the wafer W in this way, a protective film coating step is performed in which a water-soluble resin is applied to the surface that is the processed surface of the wafer W to cover the protective film. In order to perform the protective film coating step, the water-soluble resin supply nozzle 68 is formed in the central region of the processed surface of the wafer W while rotating the spinner table 48 at 10 to 100 rpm (preferably 30 to 50 rpm) as shown in FIG. Water-soluble resin 69 is dropped from the above.

  Since the spinner table 48 is rotated, the dropped water-soluble resin 69 is spin-coated on the processed surface of the wafer W, and a protective film 98 is formed on the processed surface of the wafer W as shown in FIG.

  Before the water-soluble resin 69 is spin-coated, the processed surface of the wafer W is rendered hydrophilic by irradiation with ultraviolet rays, so that the protective film 98 can be uniformly coated on the processed surface of the wafer W by spin coating. The thickness of the protective film 98 is preferably about 0.5 to 10 μm.

  The liquid resin forming the protective film 98 is preferably a water-soluble resist such as PVA (polyvinyl alcohol) PEG (polyethylene glycol), PEO (polyethylene oxide), or the like.

  If the protective film 98 is coated on the surface of the semiconductor wafer W by the protective film coating process, the spinner table 48 is positioned at the wafer loading / unloading position shown in FIG. 6 and the wafer held by the spinner table 48 is sucked and held. Is released.

  The wafer W on the spinner table 48 is transported to the chuck table 18 by the wafer transport means 16 and sucked and held by the chuck table 18. Further, the chuck table 18 moves in the X-axis direction, and the wafer W is positioned immediately below the imaging means 22.

  Image processing such as pattern matching for aligning the condenser 28 and the street S of the laser beam irradiation unit 24 that irradiates the laser beam by imaging the processing area of the wafer W by the imaging means 22 is executed. The alignment of the laser beam irradiation position is performed.

  In this way, if the street S1 or S2 of the wafer W held on the chuck table 18 is detected and the alignment of the laser beam irradiation position is performed, the condenser that irradiates the chuck table 18 with the laser beam. It moves to the laser beam irradiation region where 28 is located, and irradiates the laser beam through the protective film 98 from the condenser 28 along the street S1 or S2 of the wafer W.

  In the laser beam irradiation step, as shown in FIG. 10, from the condenser 28 of the laser beam irradiation unit 24 that irradiates the laser beam to the predetermined street S through the protective film 98 from the surface side that is the processing surface of the wafer W While irradiating the pulse laser beam, the chuck table 18 is moved in the X-axis direction at a predetermined feed rate (for example, 100 mm / second).

  The laser processing conditions are as follows, for example.

Light source: YAG laser Wavelength: 355 nm (third harmonic of YAG laser)
Output: 3.0W
Repetition frequency: 20 kHz
Condensing spot diameter: 1.0 μm
Feeding speed: 100 mm / second

  By performing the laser beam irradiation process, the laser processing groove 102 is formed along the street S on the wafer W. At this time, even if debris 100 is generated by laser beam irradiation as shown in FIG. 10, the debris 100 is blocked by the protective film 98 and does not adhere to the electronic circuit and bonding pads of the device D.

  When the laser processing groove 102 is formed in the wafer W in this way, the chuck table 18 is first returned to the position where the wafer W is sucked and held, and here, the wafer W is released from sucking and holding. Then, the wafer W is transported to the spinner table 48 of the protective film forming apparatus 30 by the transport means 32 and sucked and held by the suction chuck 48a.

  At this time, the water-soluble resin supply nozzle 68, the washing water nozzle 78, and the air nozzle 84 are positioned at a standby position separated from the upper side of the spinner table 48 as shown in FIGS.

  Then, as shown in FIG. 11, the wafer W is rotated at a low speed (for example, 300 rpm) while spraying cleaning water composed of pure water and air from a cleaning water nozzle 78 connected to the pure water source and the air source. Wash.

  As a result, since the protective film 98 coated on the surface of the wafer W is formed of a water-soluble resin, the protective film 98 can be easily washed away as shown in FIG. Debris 100 is also removed.

  When the cleaning process is completed, a drying process is performed. That is, the cleaning water nozzle 78 is positioned at the standby position, and the outlet of the air nozzle 84 is positioned above the outer peripheral portion of the wafer W held on the spinner table 48.

  Then, air is ejected from the air nozzle 84 toward the wafer W held on the spinner table 48 while rotating the spinner table 48 at, for example, 3000 rpm. At this time, the air ejected from the air nozzle 84 is swung within a swing range from a position where it hits the outer peripheral portion of the wafer W held by the spinner table 48 to a position where it hits the center portion. As a result, the surface of the wafer W is dried.

  After the wafer W is dried, the wafer W is adsorbed by the conveying means 16 and returned to the temporary storage area 12, and the wafer W is returned to the original storage location of the wafer cassette 8 by the carry-in / out means 10.

  The wafer W formed with the laser processing groove along the street S in this manner is then mounted on a braking device (expanding device) and the dicing tape T is expanded in the radial direction, so that the wafer W is laser processed. Divided into individual devices D along the grooves 102.

2 Laser processing device 18 Chuck table 24 Laser beam irradiation unit 28 Condenser 30 Protective film coating device 35 Ultraviolet irradiation device 48 Spinner table 66 Water-soluble resin coating means 68 Water-soluble resin supply nozzle 74 Cleaning means 78 Washing water nozzle 76 Drying means 84 Air nozzle

Claims (3)

A method for coating a protective film in which a processed surface of a wafer is coated with a protective film made of a water-soluble resin,
A wafer holding step for holding the wafer with a holding table having a holding surface for holding the wafer, with the non-processed surface side of the wafer facing the holding surface;
A hydrophilicity imparting step for imparting hydrophilicity to the processed surface by irradiating the processed surface of the wafer with ultraviolet rays to generate ozone and generate active oxygen;
A protective film coating step for coating the protective film by applying a water-soluble resin to the processed surface provided with hydrophilicity;
A method for coating a protective film, comprising: The holding table has a rotation axis orthogonal to the holding surface and passing through the center of the holding surface;
The method for coating a protective film according to claim 1, wherein, in the protective film coating step, the water-soluble resin is dropped onto a central region of the processed surface of the wafer while rotating the holding table. After the protective film is coated on the processed surface of the wafer by the protective film coating method according to claim 1 or 2,
A laser processing step of forming a laser processing groove by irradiating the processing surface of the wafer with a laser beam;
A protective film removing step of removing the protective film after performing the laser processing step;
A wafer laser processing method characterized by comprising:

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